Method of producing hybrid polymer-inorganic materials

ABSTRACT

Hybrid composite materials with multiscale morphologies are formed by doping polymer submicrometer spheres with semiconductor or metal (e.g. CdS or Ag, respectively) nanoparticles and using these doped microspheres as functional building blocks in production of hybrid periodically structured materials. The preparation of hybrid polymer particles include the following stages: (i) synthesis of monodisperse polymer microspheres, (ii) in-situ synthesis of the inorganic nanoparticles either on the surface, or in the bulk with polymer beads, and (iii) encapsulation of hybrid microspheres with a hydrophobic shell.

CROSS REFERENCE TO RELATED U.S. APPLICATION

This patent application relates to, and claims the priority benefitfrom, U.S. Provisional Patent Application Ser. No. 60/453,970 filed onMar. 13, 2003, which is incorporated herein by reference in itsentirety.

FIELD OF INVENTION

This invention relates to a method of producing hybrid polymer-inorganiccolloidal materials.

BACKGROUND OF THE INVENTION

There is an immense interest in hybrid nanocomposite materials withperiodic structures, since they have potential applications inproduction of photonic or photonic crystals, in optical data storage, inchemical and biochemical sensing, and in optical limiting and switching.Microbeads doped with NPs were used for biological labelling. (Han, M.;Gao, X.; Su, J. Z.; Nie, S. Nature Biotechnol. 2001, 19, 631). Photoniccrystals produced from microspheres doped with semiconductor NPs showedcoupling of structurally- and angularly-dependent electromagneticresonances (arising from microscale structural periodicity) and opticalproperties of the semiconductor quantum dots (providing spectral controlthrough the quantum confinement effect) ((a) Blanco, A.; López, C.;Mayoral, R.; Miguez, H.; Meseguer, F.; Mifsud, A.; Herrero, J. Appl.Phys. Left. 1998, 73. 1781-1783; (b) Vlasov, Yu. A.; Luterova, K.;Pelant, L; Honerlage, B.; Astratov, V. N. Appl. Phys. Lett. 1997, 71,1616-1618; (c) Lin, Y, Zhang, J.; Sargent, E. H.; Kumacheva, E. Appl.Phys. Left. 2002, 81, 3134)). Control over assembly of microspheresdoped with magnetic NPs in periodic structures was achieved under theaction of magnetic field ((a) Xu, X. L; Majetich, S. A.; Asher, S. A. J.Am. Chem. Soc. 2002, 124, 13864; (b) Lyubchanskii, I. L.; Dadoenkova, M.N.; Lyubchanskii, M. I.; Shapovalov, E. A.; Rasing, T. H. J. Phys. D.2003, 36, R277). Alternatively to solid microspheres, colloid crystalsproduced from microgels or metal NPs-doped microgels were used for thepatterning of self-assembled photonic materials. ((a) Hellweg, T.;Dewhurst, C. D.; Bruckner, E.; Kratz, K; Eimer, W. Colloid Polym. Sci.2000, 278, 972; (b) Hu, Lu, X.; Gao, J. Adv. Mater. 2001, 13, 1708; (c)Debord, J. D.; Eustis, S.; Debord, S. B,; Lofye, M. T.; Lyon, L. A. Adv.Mater. 2002, 14, 658662; (d) Lee, Y.-J,; Braun, P. V.; Adv. Mater. 2003,15, 563-566; (e) Jones, C. D.; Lyon, L. A. J. Am. Chem. Soc. 2003, 125,460)).

A “bottom-top” approach to producing materials with structural hierarchyis particularly attractive to chemists as it is a versatile and simplemethod to producing such materials. In this strategy, small structuralunits (building blocks) with useful functionalities are assembled inperiodic arrays to produce materials with periodically modulatedcomposition, structure and function.

Recently, the inventor developed a “core-shell” strategy for synthesisand fabrication of periodically structured polymer-based materials.(Kumacheva, E.; Kalinina, O.; Lilge, L. Adv. Mater. 1999, 11, 231;Kalinina, O.; Kumacheva, E. Macromolecules 1999, 32, 4122; Kalinina, O.;Kumacheva, E. Chem. Mater. 2001, 13, 35; Kalinina, O.; Kumacheva, E.Macromolecules 2002, 35, 3675). The overview of the “core-shell”approach is given in FIG. 1. Polymer or polymer-based core-shellparticles with dimensions varying from 100 nm to several microns aresynthesized in Stage A. The essential feature of these particles is aspecific relation between the glass transition temperatures, T_(g), ofthe core-forming polymer (CFP) and the shell-forming polymer (SFP); theglass transition temperature of the SFP is substantially lower than thatof the CFP, that is, T_(g,SFP)<T_(g,CFP). Following synthesis, thecore-shell microspheres are assembled in a periodic one-, two-, orthree-dimensional array (Stage B) and annealed at the temperatureT_(g,SFP)<T_(annealing)<T_(g,CFP) (Stage C). During heat processing theSFP softens, flows, and ultimately forms a continuous matrix, while theCFP remains intact. The morphology of the resulting material is shown instage C of FIG. 1.

The core-shell particles can be obtained using (a) synthesis of particlecores accompanied by the synthesis of latex shells on the surface ofcores, (b) electrostatically-driven heterocoagulation between theoppositely charged large particles of the CFP and small particles of theSFP followed by spreading of the SFP over the surface of the core duringheat processing or by (c) controlled phase separation technique (Okubo,M.; Lu, Y., Colloids Surf. A 1996, 109, 49; Ottewell, R. H., Schofield,A. B.; Waters, J. A.; Williams, N. S. Colloid Polym. Sci. 1997, 275,274; Furusawa, K., Velev, O. D. Colloids Surf. A 1999, 159, 359; Han,J.; Kumacheva, E. Langmuir 2001, 17, 7912; Li., H.; Kumacheva, E.Colloid Polym. Sci. 2003, 281, 1; Dudnik, V.; Sukhorukov, G. B.;Radtchenko, I. L.; Mohwald, H. Macromolecules 2001, 34, 2329).

The core-shell strategy provides several degrees of freedom overmorphology and composition of the ultimate material. The “compositional”degrees of freedom can be divided into two groups. First, the core andthe shells can be synthesized from the materials with distinctcompositions and properties, such as organic or inorganic polymers orconductive and dielectric organic polymers. Alternatively, theencapsulation of inorganic cores with polymeric shells producescore-shell functional building blocks for periodic mesostructured hybridmaterials.

In the second strategy, the core-shell particles are synthesized fromthe similar polymers (still keeping the required relation between theirglass transition temperatures), however, in the stage of synthesis orafter synthesis, the core and/or the shell are chemically functionalizedor physically doped with different low-molecular weight species. As aresult of confinement in the microbeads, these species form spatiallylocalized mesoscopic domains in the ultimate composite material.Fluorescent dyes, chromophores, molecules with properties useful innonlinear optics, and organic and inorganic nanoparticles can beselectively incorporated in the core-shell polymer beads thus tailoringnovel optical, magnetic or electric properties to the ultimate material.This approach is shown in FIG. 2 where the nanoparticles areincorporated in the core or the shell of the polymer beads.Alternatively, different nanoparticles can be localized in the cores andshells. Each of these combinations would lead to a particularcompositional pattern in the composite material, shown in FIG. 2.

In recent years, the modification of polymer microspheres with inorganicsemiconductor nanoparticles (NPs) has stimulated great interest inmaterials science due to the possibility of combining polymerprocessibility and intrinsic properties of NPs, such as their catalytic,magnetic and electronic properties. Polymer microbeads were synthesizedin the presence of pre-formed NPs (Kronick, P. L.; Campbell, G. L.;Joseph, K. Science 1978, 200, 1074; Frank, S.; Lauterbur, P. C. Science1993, 363, 334; Sauzedde, F.; Elaisari, A.; Pichot, C. Colloid Polym.Sci. 1999, 277, 1041; Horak, D. J. Polym. Sci. Part A Polym. Chem. 2001,39, 3707; Xu, X.; Friedman, G.; Humfeld, K. D.; Majetich, S. A.; Asher,S. A. Chem. Mater. 2002, 14, 1249) or they were mixed with preformedNPs, the latter either adsorbed to the surface of microspheres, ordiffused inside the polymer particles. (Haloui, L. I. Langmuir 2001, 17,7130).

Alternatively, NPs were synthesized in-situ, that is, inside polymerspheres, e.g., in ion-exchange resin beads or in microgel particles.(Winnik, F M.; Morneau, A.; Ziolo, R. F.; Stoever, H. D.; H.; Li, W.-H.Langmuir 1995, 11, 3660; (b) Antonietti, M.; Grohn, F.; Hartmann, J.;Bronstein, L. Angew. Chem. Int. Engl. Ed. 1997, 36, 2080).

Among these methods, the in-situ synthesis provides a higher dopinglevel, precise control over NP size and a more homogenous distributionof the NPs in the polymer microsphere.

It would be desirable to provide a method of producing compositecolloidal polymer/inorganic nanoparticle materials economically andwhich is versatile allowing one to tune the properties of thenanoparticles by changing the composition of the colloidal polymer.These colloidal polymer/inorganic nanoparticle materials could then actas the functional building blocks in fabrication of hybrid nanocompositematerials.

SUMMARY OF THE INVENTION

The present invention discloses several processes to produce multiscalehybrid polymeric/inorganic materials with periodic structures. Suchmaterials are produced by doping polymer core-shell particles withmetal, semiconductor, or magnetic nanoparticles (NPs) that weresufficiently small to provide the quantum confinement effect or achievesuperparamagnetic properties. The intrinsic feature of the methoddisclosed herein is the in-situ synthesis of the NPs on the surface orin the bulk of the polymer microspheres; this feature led to a goodcontrol over the size of the NPs by spatially localizing theirnucleation and growth sites.

In one aspect of the invention there is provided a process ofsynthesizing a composite colloidal polymer-inorganic material,comprising the steps of:

a) synthesizing a dispersion including polymer microparticles in aliquid;

b) treating said dispersion of polymer microparticles to modify an outersurface of the polymer microparticles to provide an effectiveconcentration of ligands on the outer surface of the polymermicroparticles, the ligands being selected to form a complex with atomsof a metal, ions of the metal, or molecular moieties containing themetal at the surface of the polymer microparticle;

c) adding atoms of the metal, ions of the metal, or molecular moietiescontaining the metal to the dispersion of polymer microparticles underconditions suitable to facilitate formation of a complex between theligands and the atoms of the metal, ions of the metal, or molecularmoieties at the surface of the polymer microparticles; and

d) exposing the dispersion of polymer microparticles to an effectiveagent which interacts with the atoms of a metal, ions of the metal, ormolecular moieties containing the metal to form nanoparticles on theouter surface of the polymer microparticles, the nanoparticles beingcomprised of at least the metal, the effective concentration of ligandsbeing selected to give nanoparticles with specified material properties.

In another aspect of the invention there is provided a process ofsynthesizing a composite colloidal polymer-inorganic material,comprising the steps of:

a) synthesizing a dispersion including polymer microgel particles in aliquid;

b) treating said dispersion of polymer microgel particles to modify aninterior of the polymer microgel particles to provide an effectiveconcentration of ligands in the interior of the polymer microgelparticles, the ligands being selected to form a complex with atoms of ametal, ions of the metal, or molecular moieties containing the metal inthe interior of the polymer microparticle;

c) adding atoms of the metal, ions of the metal, or molecular moietiescontaining the metal to the dispersion of polymer microgel particlesunder conditions suitable to facilitate uptake of the atoms of themetal, ions of the metal, or molecular moieties into the interior of thepolymer microgel particles;

d) exposing the dispersion of polymer microgel particles to a firsteffective agent which interacts with the atoms of the metal, ions of themetal, or molecular moieties in the interior of the polymer microgelparticles to form nanoparticles in the interior of the polymer microgelparticles, the nanoparticles being comprised of at least the metal, theeffective concentration of ligands being selected to give nanoparticleswith specified material properties;

e) exposing the polymer microgel particles to a second effective agentwhich results in the polymer microgel particles expelling the liquidtherefrom which causes the polymer microgel particles to contract involume; and

f) encapsulating the contracted polymer microgel particles with thenanoparticles in the interior thereof in a protective polymeric shellmaterial, the protective polymeric shell material being effective tosuppress interactions between the contracted polymer microgel particlesand the liquid.

In another aspect of the present invention there is provided a processof synthesizing a composite colloidal polymer-inorganic material,comprising the steps of:

a) synthesizing a dispersion including polymer microparticles in aliquid;

b) encapsulating the polymer microparticles in a shell forming polymermicrogel prepared by,

treating the polymer microparticles to provide an effectiveconcentration of ligands, the ligands being selected to form a complexwith atoms of a metal, ions of the metal, or molecular moietiescontaining the metal at the surface of the polymer microparticles,

adding atoms of the metal, ions of the metal, or molecular moietiescontaining the metal to the shell forming polymer microgel underconditions suitable to facilitate formation of a complex between theligands and the atoms of the metal, ions of the metal, or molecularmoieties at the surface of the polymer microparticles, and

exposing the polymer microgel to an effective agent which interacts withthe atoms of a metal, ions of the metal, or molecular moietiescontaining the metal to form nanoparticles dispersed throughout thepolymer microgel, the nanoparticles being comprised of at least themetal, the effective concentration of ligands being selected to givenanoparticles with specified material properties;

c) exposing the polymer microgel to a second effective agent whichresults in the polymer microgel particles expelling the liquid therefromwhich causes the polymer microgel to contract in volume around thepolymer microparticles; and

d) annealing the polymer microparticles encapsulated in the shellforming polymer microgel having the nanoparticles embedded therein toform a periodic array of polymer microgel particles.

BRIEF DESCRIPTION OF DRAWINGS

The following is a description, by way of example only, of the method ofproducing hybrid polymer-inorganic materials in accordance with thepresent invention, reference being had to the accompanying drawings, inwhich:

FIG. 1 shows a diagrammatic representation of a Prior Art “core-shell”approach to producing polymer-based nanostructured materials. A:synthesis of core-shell particles; B: assembly of core-shell particlesin periodic arrays; C: heat processing of core-shell particles atT_(g,SFP)<T_(ann)<T_(g,CFP) to produce nanocomposite material;

FIG. 2 is a diagrammatic representation showing possible localization ofnanoparticles in core-shell latex microparticles in accordance with thepresent invention: (a) inside the latex core; (b) in the shell, and (c)in the core and in the shell;

FIG. 3 a shows a synthetic route used for in-situ synthesis ofsemiconductor, metal or magnetic nanoparticles on the surface ofpoly(rnethyl methacrylate-methacrylic acid) latex beads and theirencapsulation to produce hybrid core-shell particles;

FIG. 3 b shows a synthetic route used for in-situ synthesis ofsemiconductor, metal or magnetic nanoparticles in the interior ofpoly(N-isopropyl acrylamide-acrylic acid-2-hydroxyethyl acrylate)microgels;

FIG. 4 shows scanning electron micrographs SEM images of (a) PMMA-PMAAbeads; PMMA/PMAA weight ratio is 5/1, pH=4.55; (b) PS-PAA beads; PS/PAAratio is 1/1, pH=3.45; (c) size distribution of PMMA-PMAA latexparticles (I); PS/PAA latex particles (II), poly(NIPAM-AA-HEA) microgels(III) at (NIPAM/AA/HEA ratio is 1/0.22/0.5, pH=4.45);

FIG. 5 shows transmission electron micrographs (TEM) images of NP-dopedpolymer microspheres: PMMA-PMAA beads coated with (a) CdS NPs, (b) AgNPs (PMMA/PMAA weight ratio 5/1, pH=6.5); PS-PAA microgels doped with(c) CdS NPs, (d) Ag NPs (PS/PAA weight ratio 1/1, pH=6.7;poly(NIPAM-AA-HEA) microgels doped with (e) CdS NPs, (f) Ag NPs(PNIPAM/PAA/PHEA weight ratio is 1/0.22/0.5, pH=6.5);

FIG. 6 a, b shows ultraviolet (UV)-visible spectra (a) andphotoluminescence spectra (b) of CdS nanoparticles synthesized on thesurface of PMMA-PMAA microspheres shown in FIG. 5 a. PMMA/PAA weightratio is 0.44. λ_(ex)=380 nm;

FIG. 6 c shows UV-Visible absorbance of Ag nanoparticles synthesized onthe surface of PMMA-PMAA microspheres. PMMA/PAA weight ratio is 0.44.

FIG. 6 d,e shows UV-Visible absorbance (d) and photoluminescence spectra(e) of CdS NPs synthesized in PNIPAM/PAA/PHEA microgels before (-) andafter heat processing ( - - - ). [PAA]/[PHEA]/[PNIPAM]=0.36/0.13/1,[BIS]=4 mol %; [COOH]/[Cd²⁺]/[S²⁻]=110.5/0.5. From top to bottom CdSconcentration in microgels is 0.027 (A), 0.054 (8), and 0.08 (C) g/gpolymer. A rising baseline characteristic of semiconductor nanoparticlesobscures absorption data at wavelengths significantly lower than theabsorption maximum. λ_(ex)=380 nm. λ_(ex)=380 nm.

FIG. 6 f shows the UV-Visible absorbance spectra of Ag nanoparticelssynthesized in poly(NIPAM/AA/HEA) microgels Ag NP concentration inmicrogel: 0.23 g/g polymer (bottom spectrum), 0.39 g/g polymer (topspectrum). Microgel composition as in FIG. 6 d, e.

FIG. 7 a shows the variation in diameter of poly (NIPAM-AA-HEA) microgelparticles (⋄) and in the concentration of CdS NPs in microgel (♦)plotted versus variation in pH, the molar ratio [AA]/[HEA]/[NIPAM] is0.36/0.13/1; [COOH]/[Cd²⁺]/[S²⁻]=1/0.5/0.5; [BIS]=4 mol %;

FIG. 7 b shows the variation in concentration of CdS NPs in microgels(⋄) and in microgel size (∘) plotted versus (a) fraction of AA inmicrogels for molar ratio [HEA]/[NIPAM]0.54; [BIS]=4 mol %;

FIG. 7 c shows the variation in concentration of CdS NPs in microgels asa function of fraction of HEA in microgels for [AA]/[NIPAM]=0.36;[BIS]=4 mol %;

FIG. 7 d shows the variation in concentration of CdS NPs in microgels asa function of concentration of crosslinking agent for[AA]/[HEA]/[NIPAM]=0.36/0.13/1, the molar ratio [COOH]/[Cd²⁺]/[S²⁻] was1/0.5/0.5 and the microgels were ionized at pH=8.3;

FIG. 7 e shows the variation in CdS NP concentration in microgel as afunction of molar ratio [Cd²⁺]/[COOH], the microgel composition was:[AA]/[HEA]/[NIPAM]=0.36/0.13/1, [BIS]=4 mol % (♦);[AA]/[HEA]/[NIPAM]=1.03/0.13/1; [BIS]=4 mol % (▴), and the microgelparticles were ionized at pH=8.3;

FIG. 7 f shows the variation in CdS NP concentration in microgel as afunction of molar ratio [S²⁻]/[Cd²⁺], the microgel composition was:[AA]/[HEA]/[NIPAM]=0.36/0.13/1, [BIS]=4 mol % (♦);[AA]/[HEA]/[NIPAM]=1.03/0.13/1; [BIS]=4 mol % (▴), and microgelparticles were ionized at pH=8.3.

FIG. 8 shows an X-ray powder diffraction patterns of microgels dopedwith CdS (top) and Fe₃O₄ NPs. Microgel compositions:[AA]/[HEA]/[NIPAM]=0.36/0.13/1, [BIS]=4 mol %;[COOH]/[Cd²⁺]/[S²⁻]=1/0.5/0.5. CdS concentration in microgel is 0.027g/g polymer; Fe₃O₄ concentration in microgel is 0.724 g/g polymer.

FIG. 9 a is an SEM micrograph of colloid crystals obtained from 285nm-size PMMA/PMAA latex particles coated with in-situ synthesized CdSnanoparticles. 2.5 μm

FIG. 9 b shows the reciprocal of optical transmission of colloid crystalfabricated from bare (curve 1) and CdS-doped (curve 2) PMMA/PMAA latexmicrospheres (shown in FIG. 9 a).

FIG. 10 shows a laser confocal fluorescent microscopy (LCFM) image ofhybrid CdS-polymer nanocomposite obtained from CdS-doped PMMA-PMMA-PBMAcore-shell particles with the image taken 10 μm below the surface of thefilm. CdS was excited by UV light at λ=364 nm; Scale bar is 2 μm.

FIG. 11 a is the variation in microgel diameter as a functrion oftemperature at pH=4.2. Open and solid symbols correspond topoly(NIPAM-M-HEA) microgel and poly(NIPAM-AA-HEA) microgel doped withCdS NPs, respectively. AA/NIPAM weight ratio 0.44 (⋄,♦), 0.22 (Δ,▴) and0.11 (∘,).

FIG. 11 b gives the variation in diameter of hybrid core-shell particlesas a functrion of temperature at pH=4.2 after encapsulation with ahydrophobic poly(MMA-BMA-AA) core, the weight ratio MMA/BMA/AA) is15/4/1 and the AA/NIPAM weight ratio 0.44 (⋄,♦), 0.22 (Δ,▴) and 0.11(∘,);

FIG. 11 c is an SEM micrograph of colloid crystals obtained from 580nm-size core-shell particles with 305 nm-size poly(NIPAM-AA-HEA) coresdoped with CdS NPs (φ=0.44), and

FIG. 11 d is an optical transmission spectrum of the colloid crystals ofFIG. 9 a.

FIG. 12 shows the magnetic properties of Fe₃O₄ NPs in the interior ofdried poly(NIPAM-AA-HEA) microgel, the NP concentration is 0.724 g/gpolymer, T=300 K, and the microgel composition [NIPAM]=0.36/0.13/1,[BIS]=4 mol %; [COOH]/[Cd²⁺]/[S²⁻]=1/0.5/0.5.

DETAILED DESCRIPTION OF THE INVENTION Abbreviations:

PMMA is poly(methyl methacrylate); PBMA is poly(butyl methacrylate); PSis polystyrene; PMAA is poly(methyl methacrylic acid); AA is acrylicacid; PM is polyacrylic acid; NIPAM is N-isopropyl acrylamide; PNIPAM ispoly(isopropyl acrylamide); HEA is 2-hydroxyethyl acrylate; PHEA ispoly(2-hydroxyethyl acrylate); Poly(NIPAM-AA-HEA) is poly(N-isopropylacrylamide-acrylic acid-2-hydroxyethyl acrylate).

The present invention provides a method for synthesizing polymer-basedcolloidal microparticles having inorganic nanoparticles grown either inthe interior of the microparticles or on the surface of themicroparticles. The method can be used to control material properties ofthe inorganic nanoparticles such as nanoparticle size, crystallinity andmorphology, a critical feature controlling various electronic, opticaland magnetic properties of the resulting colloidal microparticles.

In one embodiment of the invention hybrid core-shell polymermicrospheres comprised of microparticle cores covered with a polymericshell are used as the functional building units in production ofmultiscale hybrid polymer-based materials. The synthesis of theinorganic nanoparticles may be conducted in different stages of thepreparation of polymer core-shell particles so that the nanoparticlesmay be (a) incorporated in the microparticle core, (ii) localized at theinterface between the core and the shell, or (iii) introduced in theparticle shell. The material may be produced with the nanoparticlesincorporated into the shell structure in a manner similar to theincorporation of nanoparticles in the core: making a gel-like shell,synthesizing nanoparticles, and the collapsing (shrinking) the gel-likeshell.

The method of the present invention has been exemplified using threetypes of inorganic nanoparticles, namely semiconductor (CdS), the puremetal (Ag) and magnetic (Fe₃O₄) nanoparticles. CdS nanocrystals with a 6nm exciton diameter and a 2.5 eV band gap (Henglein, A. J. Phys. Chem.1982, 86, 2291) show potential applications in solar cells and nonlinearoptics devices, whereas electronic properties of Ag nanocrystals can beutilized in catalysis, optical switching and optical storage devices(Belloni, J. Curr. Opin. Colliod Interf. Sal. 1996, 1, 184). Microgelsdoped with and magnetic Fe₃O₄ nanoparticles can be used in separationtechniques and drug delivery systems.

FIGS. 3 a shows a synthetic route used for the preparation of polymermicrobeads doped with CdS nanoparticles. FIG. 3 b shows the syntheticroute to the preparation of semiconductor, metal and metal oxidenanoparticles in the interior of microgels. All routes involved thepreparation of the polymer microspheres containing carboxyl groups,deprotonation of COOH groups, ion exchange between the counter-ions inthe double electrical layer of the microbeads and metal ions from theintervening medium, the reaction between cations and anions leading tothe formation of semiconductor nanoparticles, reduction of cations toproduce metal nanoparticles or oxidation of cations to obtain metaloxide (magnetic) nanoparticles. This step could be followed byencapsulation of the nanoparticle-modified mesospheres with a polymericshell. The difference, between the two routes shown in FIG. 3 a and FIG.3 b was in the localization of the nanoparticles. For the condensedlatex beads (FIG. 3 a) the nanoparticles were synthesized on the surfaceof the microspheres, whereas when polymer microgel particles were usedas microreactors, the nanoparticles were synthesized in the bulk of themicrospheres (FIG. 3 b).

For the synthesis of Ag nanoparticles following an increase in pH toionize carboxyl groups, the latex dispersion or the microgel dispersionwas treated with an aqueous solution of AgNO₃. NaBH₄ was then added asthe reducing agent at 0° C.

Magnetic Fe₃O₄ NPs were prepared in the interior of microgels using aco-precipitation technique. A 1.0 M aqueous KOH solution was added to200 ml of poly(NIPAM-AA-HEA) microgel dispersion ([COOH]=3.0 mM) toachieve pH=6.3±0.3. The system was purged with N₂, mixed with 1.05 g ofFeSO₄.7H₂O and stirred overnight. After dialyzing the dispersion under aN₂ atmosphere, 0.104 g of NaNO₂ was added under stirring. Then, 12.5 mLof 28 wt % ammonia solution was quickly introduced into the system undervigorous stirring. The color of the dispersion became green and afterca. 2 h turned to black. The resulting dispersion was dialyzed againstthe deionized water under a N₂ atmosphere.

The polymer colloidal microparticles particles were prepared usingstyrene, methyl methacrylate (MMA), methacrylic acid (MAA), acrylic acid(AA), 2-hydroxyethyl acrylate (HEA), butyl acrylate (BA), butylmethacrylate (BMA), and ethylene glycol dimethacrylate (EGDMA) purchasedfrom Aldrich Canada. All monomers were purified by vacuum distillation.N-isopropyl acrylarnide (NIPAM, Scientific Polymer Products, Inc.),N,N′-methylenebisacrylamide (BIS), potassium persulfata (KPS), potassiumhydroxide (KOH), cadmium perchlorate hydrate (Cd(ClO4)₂.xH₂O, sodiumdodecyl sulfate (SDS), sodium sulfide nonohydrate (Na₂S.9H₂O), silvernitrate (AgNO₃), sodium borohydride (NaBH₄) (all from Aldrich Canada),2,2′-azobis(2-methyl propionitrile) (AIBN, Kodak), andisooctyl-3-mercaptopropionate (IOMP, TCI America) were used as received.The water was deionized to 18.2 MΩ·cm and pH≈5.5 (Millipore Milli-Q).

Three types of monodisperse microspheres were used including 1)poly(methyl methacrylate-methacrylic acid) (PMMA-PMAA) latex, 2)crosslinked poly(styrane-acrylic acid) (PS-PM) latexes transforming to amicrogel at high pH, and 3) poly(N-isopropyl acrylamide-acrylicacid-2-hydroxyethyl acrylate) (PNIPAM-PAA-PHEA) microgels. It will beunderstood that while a preferred embodiment of the present inventionuses substantially monodisperse microspheres, the invention is notlimited to microspheres, but other colloidal particle shapes may beused, e.g. ellipsoidal, rods and the like.

PMMA-PMAA and PS-PAA particles were prepared using surfactant-freeemulsion polymerization. Both dispersions were purified bycentrifugation, decantation, redispersion in the deionized water, anddialysis against water.

The PNIPAM-PAA-PEHA microgels were prepared by precipitationpolymerization in aqueous solutions in the presence of a small amount ofSDS. (Pelton, R. H.; Chibante, P. Colloids Surf. 1986, 20, 247; Pelton,R. Adv. Colloid Polym. Interf. Sci. 2000, 85, 1). To remove SDS andother impurities, the dispersion was purified to by successivecentrifugation, decantation, redispersion in the deionized water, anddialysis.

For the synthesis of CdS NPs on the surface of PMMA-PMAA beads, thelatex dispersion with ca. 20 wt % of polymer particles was treated with0.1M KOH solution, dialyzed to pH=8.5, treated with a 1M solution ofCd(ClO₄)₂ and then maintained under stirring for 4 h. The liquid mediumwith unreacted Cd²⁺-ions was removed by centrifugation; following thisstep the precipitate was redispersed in the deionized water. Then, a 1Maqueous solution of Na₂S was slowly introduced into the dispersion understirring. The resulting dispersion was centrifuged, redispersed inwater, and dialysed. Following dialysis, the dispersion preserved ayellow or orange color, which indicated that CdS nanoparticles were notremoved from the surface of latex beads.

For the synthesis of Ag nanoparicles on the surface of polymermicrobeads, after addition of KOH and dialysis, a 0.1 M aqueous solutionof AgNO₃ was added to the dialyzed dispersion. Following severalcentrifugation-redispersion cycles, Ag⁺-ions incorporated in the doubleelectrical layer of the latex particles were reduced at 0° C. using afreshly prepared 0.1M aqueous solution of NaSH₄. The dispersioninstantly became dark-brown. After stirring overnight, the dispersionwas purified by centrifugation (to remove unattached Ag nanoparticles)and then dialyzed.

The preparation of PS-PM and POLY(NIPAM-AA-HEA) microgels doped with CdSand nanoparticles was very similar, however the polymer dispersions weresignificantly more dilute and they contained only 1-2 wt % of thepolymer particles although concentrations up to 15% may be used.

Once the core polymer microparticles with the nanoparticles on thesurface or in the interior were prepared, hybrid core-shell particleswere prepared by surfactant-free emulsion polymerization of theshell-forming polymer on the surface of the NP-modified cores. PMMA-PMAAmicrobeads coated with CdS or Ag NPs were used as seeds for interfacialpolymerization of poly(methyl methacrylate)-poly(butyl methacrylate)shell (weight ratio poly(methyl methacrylate)/poly(butyl methacrylate)was 1/1). PS-PAA cores doped with NPs were encapsulated withpolystyrene-poly(methyl methacrylate)-polyacrylic acid-poly(butylmethacrylate) copolymer (weight ratio 2.5/10/1/2.5, respectively).Hybrid PNIPAM-PAA-PEHA cores were encapsulated with a hydrophobicpoly(methyl methacrylate)-poly(butyl acrylate)-polyacrylic acid shell(weight ratio 15/4/1, respectively).

The concentration of carboxyl groups (COOH) in the polymer microsphereswas determined by potentiometric titration (using a method disclosed inMakino, K.; Agate, H.; Ohshima, H. J. Colloid Interf. Sci. 2000, 230,128) using a PH/mV/TEMP meter (Model P25, EcoMet Inc, USA). Thefreeze-dried sample (0.1 g) was re-dissolved in 0.1 M aqueous solutionof sodium hydroxide (NaOH, 20 mL) and stirred overnight. The excess NaOHwas titrated with a 0.05M aqueous HCl solution.

The dimensions and polydispersity of the core polymer particles weremeasured using photon correlation spectroscopy (PCS) (Zetasizer3000HS_(A), Malvern Instruments, U. K.). For each temperature, thedispersions of microparticles were equilibrated for 30 min.

A Varian Cary 500 spectrophotometer was used to obtain UV-Vis absorptionspectra of the NPs incorporated in the polymer microspheres. Generally,to suppress scattering the dispersions of PMMA-PMAA or PS-PAA beads werediluted with dimethyl sulfoxide, a solvent with a high refractive index(n=1.4790). Photoluminescence spectra of CdS NPs were acquired on a SpeeFluoroMax spectrometer (λ=380 nm).

The morphology of the hybrid microspheres was studied on gold-coatedsamples using a Hitachi S-570 scanning electron microscope (SEM)operated at an acceleration voltage of 15 kV, and a Hitachi 600transmission electron microscope (TEM) at 70 kV. The TEM samples wereprepared by placing a small drop of the aqueous suspension on a carbonfilm supported by a copper grid (Electron Microscope Sciences, Inc., PA,USA). High-resolution TEM images were obtained using a JEOL 2010Fmicroscope operated at 200 kV. The morphology of the material producedfrom the polymer microspheres doped with CdS NPs was studied by LCFMusing a Carl Zeiss LSM510 confocal microscope with lateral and thevertical resolutions of 0.23 and 0.29 μm, respectively. The 364 nm linewas employed for the excitation of the fluorescent dye. All images wereanalyzed using the ImageTool for Windows (Version 1.28) software(Univeristy of Texas, Health Science Center, San Antonio, USA).

The structure of CdS and Fe₃O₄ NPs was characterized using X-ray powderdiffraction (X'Pert Philips Materials Research Diffractomer) using CuK_(α) radiation (λ=1.54178 Å) at 40 kV and 50 mA at a scanning speed of0.02° s⁻¹ in the 2θ range 5-75°.

Measurements of magnetic properties of Fe₃O₄ NPs were carried out on aQuantum Design, Inc. Model PPMS-9 superconducting quantum interferencedevice (SQUID) susceptometer at 300 K.

The size and monodispersity of polymer microspheres were importantparameters in production of hybrid composite materials with periodicstructures, since they determined the characteristic length scale andperiodicity of the ultimate material. In addition, the amount orconcentration of carboxyl groups on the surface or in the bulk of thepolymer particles was vital in synthesis of nanoparticles. Therefore,these three parameters were chosen as the main criteria in synthesis ofpolymer micropsheres. The concentration of carboxyl groups is importantbecause the nucleation and growth of the nanoparticles is determined bythe spatial localization of carboxyl groups: too low a concentration ofcarboxyl groups leads to the formation of large nanoparticles separatedby large distances, whereas too high a concentration of carboxyl groupsresults in a very small distance the nucleation sites and thenanoparticles aggregate.

Since the polymerization reaction occurred in a starve-fed regime (thatis, the ratio of the polymer constituents in the polymer micropshereswas the same as in the monomeric mixture added to the reactor), theconcentration of COOH groups was determined by the weight ratio of thereacting monomers. Generally, the weight ratio PMMA/PMAA varied from10/1 to 4/1. The diameter of the latex particles varied from 150 to 600nm. FIG. 4 a shows the SEM image of the PMMA-PMAA microspheres obtainedfor PMMA/PMAA weight ratio 5/1, whereas FIG. 4 c, curve (I) shows thesize distribution of these beads.

To obtain a stable dispersion of PS-PAA latex, the weight ratio PS/PAAwas generally 1/1, that is, the fraction of PM was relatively high.Following polymerization conducted at pH=3.45, the diameter of themicrospheres was ca 450 nm. The SEM image and the size distribution ofthese microspheres are shown in FIGS. 4 b and 4 c (curve (II),respectively. The dimensions of the PS-PAA latex showed a strongdependence on pH: following increase in pH from 3.45 (reactionconditions) to 10, the dimensions of the latex beads increased from 450to 680 nm. Such increase in size was caused by the deprotonation of PAAin the microparticles, which resulted in a strong repulsion between thepolymer chains and conversion of the latex particles into a microgel.

In contrast to PS-PAA microbeads transformed into microgels at elevatedpH by ionization of carboxyl groups of PM, the Poly(NIPAM-AA-HEA)particles were synthesized as a microgel. The particle size andpolydispersity depended on several factors, such as the weight ratioNIPAM/AA/HEA, and SDS and BIS concentration. Generally, the diameter ofmicrogels varied from 200 to 500 nm, as determined by photon correlationspectroscopy. A typical size distribution curve of the NIPAM/AA/HEAmicrogel is shown in FIG. 4 c (III). The SEM image of thePoly(NIPAM-AA-HEA) microgels is unavailable due to spreading of thepolymer on the SEM stubs.

The ionization of carboxyl groups was a crucial step of the approachused in the present work. The optimum extent of ionization depended onthe type of the NPs and the desired doping level of the microsphereswith NPs. Generally, the range of pH was determined by the following twofactors. Increase in extent of protonation of acid groups in the polymermicrospheres (that is, increase in pH) led to the increase in the rateand extent of ion uptake from the liquid medium (a) Clay, R. T.; Cohen,R. E. Supermol. Sci. 1998, 5, 41. (b) Kane, R. S.; Cohen, R. E.; Silbey,R. Chem. Mater. 1999, 11, 90). On the other hand, the maximum value ofpH was limited by the solubility of the corresponding metal hydroxides,that is, by the value of the solubility product constant K_(sp). Forexample, K_(sp) of Cd(OH)₂ was 7.2×10⁻¹⁵ and generally, the maximumvalue of pH did not exceed 8.6 (CRC Handbook of Chemistry and Physics,81st ed.; CRC Press: Cleveland, 2000).

Following synthesis of the nanoparticles, the size and polydispersity ofthe PMMA-PMAA beads underwent a very insignificant change. FIGS. 5 a and5 b shows representative TEM images of the polymer microspheres dopedwith CdS and Ag nanoparticles. In FIGS. 5 a and 5 b, 580-nm sizePMMA-PMAA microspheres are uniformly coated with CdS and Ag NPs,respectively. Image analysis of the TEM micrographs showed that ca. 40%of the area of the latex beads was covered with the NPs. The size of thenanoparticles varied from 4 to 7 (CdS NPs) and from 4 to 5 nm (Ag NPs),depending on the PAA fraction in the polymer microspheres and on themolar ratios [COOH]/[Cd²⁺] and [Cd²]/[S²].

The PS-PAA microgels doped with CdS or Ag nanoparticles (FIGS. 5 c and 5d) had similar morphologies. The dimensions of CdS and Ag nanoparticlessynthesized in PS-PAA microgels were 5±1 and 4±1 nm, respectively,whereas their concentrations (obtained from image analysis) were 52 and47 vol %, respectively. This doping level was lower than thatanticipated from the stoichiometric ratio COOH⁻/Cd²⁺ or COOH⁻/Ag⁺,perhaps, because diffusion of the metal ions in the hydrophobicpolystyrene environment was suppressed. A multi-step doping process didnot lead to significant increase in concentration of the nanoparticlesin PS-PAA microgel. FIGS. 5 e and 5 f show TEM images of microgels dopedwith CdS and Ag nanoparticles, respectively. The average size of the CdSnanocrystals varied from 4 to 6 nm, while Ag nanoparticles were 2-3 nmlarge. On the basis of image analysis, loading of the microgel sphereswith nanoparticles increased with increasing polyacrylic acidconcentration and it could reach up to ca. 10 vol %. The dimensions ofCdS nanoparticles in the microspheres could also be controlled byvarying φ: increase in weight fraction of polyacrylic acid in themicrogel increased the number of NP nucleation sites, which led to thereduction of nanoparticle size.

The dimensions of Ag and CdS nanoparticles synthesized on the surface orin the bulk of the polymer microbeads were further characterized byUV-visible spectroscopy. The absorption spectrum of the CdSnanoparticles on the surface of PMMA-PMAA microbeads is shown in FIG. 6a. The maximum centered around 486 nm corresponded to the average sizeof CdS NPs of 5.0 nm, while the edge at 515 nm was related to thelargest size of CdS NPs of ca. 6.8 nm, (Spanhel, L.; Haase, M.; Weller,H.; Henglein, A. J. Am. Chem. Soc. 1987, 109, 5649; Moffitt, M.; Vali,H.; Eisenberg, A. Chem. Mater. 1998, 10, 1021), in reasonable agreementwith the results obtained by TEM.

The very small Ag nanoparticles, upon illumination with UV light exhibitfluorescence (data not shown). This is the intrinsic property of verysmall NPs, which was achieved because of the in-situ synthesis.

The photoluminescence spectrum of CdS nanoparticle is shown in FIG. 6 b.Photoluminescence was excited at 380 nm. The emission peak appearsaround 525 nm, and a long tail extended into 650 nm, similar to thatreported by Lopez at al (A. Blanco, C. López, R. Mayoral, H. Miguez, F.Meseguer, A. Mifsud, and J. Herrero, Appl. Phys. Lett. Lett. 1998 73,1781.)

FIG. 6 c shows the UV-visible spectrum of Ag nanoparticles. Theexistence of a single absorption peak at 430 nm was close to the valuemeasured by Wang, W. and Asher, S. A. J. Am. Chem. Soc. 2001, 123, 12528and Dai and J.; Bruening, M. L. Nano Lett. 2002, 2, 497 for 2.5 nm of Agquantum dots.

FIGS. 6 d and 6 e show UV-Vis spectra (d) and photoluminescence spectra(e) of CdS nanoparticles synthesized in POLY(NIPAM-AA-HEA) microgels,respectively, before and after heat processing. In FIG. 6 e Increasingloading of microgels with nanoparticles led to red-shift of absorptiononset from 430 to 500 nm, indicating increase in NP size. Nevertheless,in all samples the onset of absorption was below 510 nm (measured forbulk CdS), suggesting the quantum confinement effect. Based on the NPsize-absorption relation (Moffitt, M. L.; McMahon, P. V.; Eisenberg, A.Chem. Mater. 1995, 7, 1185-1192; Moffitt, M.; Vali, H.; Eisenberg, A.Chem. Mater. 1998, 10, 1021-1028; Zhao, H.; Douglas, E. P. Chem. Mater.2002, 14, 1418-1423) the size of CdS nanoparticles varied from 3.0 to5.9 nm, similar to the results of TEM image analysis. The dispersions ofhybrid microgels were refluxed at for 12 h to refine the NP crystallinestructure and improve their size distribution. The correspondingabsorption spectra (dotted lines) show a sharper onset of absorption andappearance of absorption peaks, indicating enhanced NP size distributiondue to Ostwald ripening of smaller nanoparticles. We note that thiseffect was more marked for NPs embedded in a lower amount in hybridmicrogels.

FIG. 6 e shows photoluminescence (PL) spectra of CdS NPs in the interiorof microgels. The PL emission bands (bottom to top, solid lines)red-shifted and their intensity increased with increase in NPconcentration in microgels. For higher NP concentration the PL spectrafeatured two well-resolved peaks. The shorter wavelength emission bandswere ascribed to band gap PL of CdS NPs, since they coincided withabsorption onset of these samples (FIG. 6 e). The longer wavelength PLemission peaks resulted from the interstitial sulfur or cadmiumvacancies. The relative intensity of these two peaks changed withincrease in NP concentration and size. The width of PL bands of ca.100-160 nm was similar or only slightly broader than that measured forthe CdS NPs synthesized using starburst dendrimerslinear and brunchedpolymer stabilizers, and block copolymer micelles. The PL emission bandsof CdS NPs showed a notable red-shift after heat treatment of hybridmicrogels (FIG. 6 e, dotted spectra). For microgels with a lowconcentration of NPs the PL peak shifted from 485 to 566 nm and thecolor of microgel changed from blue to yellow. The PL emission bands ofhybrid microgels with a higher concentration of CdS NPs after heatprocessing featured a single broad PL peak. Since post heat processingof hybrid microgels improved NP size distribution (FIG. 6 e), we ascribethese emission bands to the recombination of electrons trapped in asulfur vacancy with a hole in the valence band of CdS. The color ofthese rnicrogels after refluxing turned from green to orange or red.Thus by changing NP concentration in microgels and by using post heattreatment we obtained hybrid rnicrogels with PL emission tunable in theentire visible spectral range.

FIG. 6 f shows UV-Visible absorbance shows UV-Visible absorbance spectraof Ag NPs synthesized in the interior of in poly(NIPAM-AA-HEA)microgels. A well-defined surface plasmon resonance was measured at 411nm (bottom spectrum), similar to that measured for ca. 2.5 nm-size AgNPs by Asher at (Wang, W. and Asher, S. A. J. Am. Chem. Soc. 2001, 123,12528). In microspheres with a lower concentration of Ag NPs (or smallerNP size) absorption peak broadened due to the “intrinsic size effect” inmetal NPs (Mulvaney, P. Langmuir. 1996, 12, 788-800).

FIG. 7 a shows that increase in pH in the first step of nanoparticlesynthesis led to a gradual increase in concentration of CdS NPs in themicrogel. Stronger ionization of carboxyl groups of polyacrylic acidincreased the driving force for the incorporation of cations into themicrospheres. In addition, microgel size (and hence microgel voids)increased with pH: in the range 2.3<pH<9.2 the hydrodynamic radius ofmicrogel particles increased from ca. 230 to 600 nm. For polyacrylicacid pK_(a)=4.75 (Encyclopedia Polym. Sci. Eng., 2-nd edn., Ed. J. I.Kroschwitz, John Wiley and Sons, 1985; p. 212) thus the carboxyl groupswere completely ionized at pH ≧6.

Further increase in microgel size for 6.0<pH<9.2 occurred due to thechange in conformation of polyacrylic acid fragments from a highlycompact structure to an expanded coil conformation. The range 6<pH<9 wasnot, however, realized in the NP synthesis due to the formation ofinsoluble metal hydroxides at elevated pH. The threshold values of pH insynthesis of CdS, Ag and Fe₃O₄ NPs were bound by the values ofsolubility products (Lang's Handbook of Chemistry, 15th ed., Section 8,Dean, J. A., Ed., McGraw Hill: New York, 1999):K_(sp,Cd(OH)2)=7.2×10⁻¹⁵, K_(sp,AgOH)=2.0×10⁻⁸, andK_(sp,Fe(OH)2)=4.87×10⁻¹⁷, respectively. For example, the upper valuesof pH were 8.35 for [Cd²⁺]=1.5 mM, 8.8 for [Ag⁺]=3 mM and 7.1 for[Fe²⁺]=1.5 mM.

The concentration of CdS NPs in the microgels was further controlled bychanging the concentration PAA, PHEA and BIS in microgels (FIG. 7 b-d)The variation in microgel size is given in the same figure. Withincreasing the amount of PAA and BIS in microgels the variation inconcentration of CdS nanoparticles followed the trend in change ofmicrogel size. In addition, increase in amount of PAA in microgelsincreased the affinity of Cd²⁺-ions to microgels, which in turn,resulted in increase of CdS concentration. In contrast, increase in PHEAfraction resulted in decreased loading of microgels with CdS NPs(despite increasing microsphere size) because of the hydrophobic natureof PHEA and a reduced amount of AA fraction.

The concentration of CdS NPs in the microgels was further controlled bychanging the molar ratio [Cd²⁺]/[COOH] (FIG. 7 e). The doping level ofNPs was however lower than the value estimated from the stoichiometricratio ([COOH]/[Cd²⁺]=1/0.5: generally, only 77.5±12.5% of carboxylgroups reacted with Cd²⁺-cations, even when the latter were added inexcess. Therefore, following the introduction of metal ions in themicrogel, the dispersion was dialyzed to remove free metal ions.

FIG. 7 f shows the variation in the concentration of CdS NPs inmicrogels versus the molar ratio [S²⁻]/[Cd²⁺]. For [S²⁻]/[Cd²⁺]≦1,microgel doping level linearly increased with [S²⁻]/[Cd²⁺]; whereas for[S²⁻]/[Cd²⁺]>1, no notable change in CdS loading was observed,suggesting that S²⁻-anions added in excess did not take part in theformation of CdS NPs.

The structure of CdS— and Fe₃O₄ NPs synthesized in the interior ofmicrogels was characterized using X-ray powder diffraction (XRD). InFIG. 8 the top XRD pattern of the CdS NPs exhibits characteristic peaksat scattering angles (2θ) of 26.4°, 43.9° and 51.9°, corresponding toscattering from the {111}, {220} and {311} planes, respectively, of acubic CdS crystal lattice (the standard card JCPDS file #10-0454). Weakbroadening of the diffraction peaks occurred due to the small NP size.The average nanocrystal size calculated using Scherrer equation^(i) was3.1 nm, consistent with the results obtained for the same sample fromTEM image analysis. The bottom pattern in FIG. 6 shows XRD results forFe₃O₄ NPs. The XRD patterns of magnetite (Fe₃O₄, JCPDS file #88-0315)and maghemite (γ-Fe₉O₃, JCPDS file #39-1346) are similar: they can beidentified by comparing peak intensities. The data suggested that thenanocrystals synthesized in microgel templates were Fe₃O₄ NPs. Weassigned the measured peak positions at their relative intensities(30.07° (28), 35.44° (100), 43.06° (20), 56.93° (25) and 62.64° (34)) tothe {220}, {311}, {400}, {511} and {440} planes of Fe₃O₄ lattice,respectively. The mean crystallite size was 8.1 nm, (X-ray DiffractionProcedures, Klug, H. P.; Alexander L. E.; John Wiley: New York, 1959) inagreement with TEM image analysis.

High monodispersity and negative surface charge of the latex particlescoated with CdS nanoparticles were beneficial for colloidcrystallization. SEM imaging showed that the core-shell microbeads dopedwith CdS or Ag nanoparticles formed multilayer colloid crystals. FIG. 9a shows a fragment of the colloid crystal obtained from 285-nm sizecore-shell particles containing 305 nm-size poly(NIPAM-AA-HEA) coatedwith CdS nanoparticles, while FIG. 9 b shows the optical transmissionspectrum measured for these crystals at normal incidence (θ=0°) to the(111) plane of the colloid crystals fabricated from the uncoated(curve 1) and CdS-doped particles (curve 2), respectively. For the arrayof 285 nm PMMA/PMAA microspheres a diffraction peak appeared at 631 nm,whereas when the same spheres were doped with CdS NPs the peak shiftedto 656 nm. For such crystals the relation between the spectral positionof the diffraction peak, λ_(c), and the effective refractive index,n_(eff), is λX_(c)=1.632 n_(eff) D where D is the diameter of amicrosphere. Since the colloid crystals obtained from the modified anduncoated microbeads had a similar lattice constant, we estimated a 4%increase in effective refractive index, in comparison with the arrayformed by unmodified PMMA/PMAA beads. The effective refractive indicesof the bare and CdS-coated particles were 1.357 and 1.410, respectively.Furthermore, the amount of CdS NPs in the latex microspheres wascalculated from the value of n_(eff) of the CdS-doped colloid crystalassuming volume fraction of PMMA-PMAA beads to be 74% and using therelationship n_(eff) ²=0.26n_(a) ²+n_(PMMA/PMAA) ²(0.74−f)+n_(NP) ²fwhere n_(a), n_(PMMA/PMAA), and n_(NP) are the refractive indices ofair, PMMA/PMAA, and CdS, respectively, and f is the volume fraction ofCdS in the colloid crystal. For n_(PMMA/PMAA)=1.491 and n_(NP)=2.5, fwas found to be 0.021 and CdS/polymer volume ratio in the microsphereswas 2.9 vol %.

In order to act as the functional building blocks in the “core-shell”approach (FIG. 1), hybrid nanoparticles-doped polymer microspheres hadto be encapsulated with a shell-forming polymer. For the doped microgelspheres this step was also important in suppressing their hydrophilicnature, a serious obstacle in potential applications of these particles.

Relatively hydrophobic PMMA-PMAA and PS-PAA microspheres doped with CdSand Ag nanoparticles acted as seeds in emulsion polymerization. Thepresence of the inorganic nanoparticles on the surface of hybrid coresdid not notably suppress interfacial polymerization. For the PMMA-PMAAhybrid cores the SFP was synthesized from a poly(methylmethacrylate)-poly(butyl methacrylate) (PMMA-PBMA) copolymer. Thepresence of PMMA in the latex shell resulted in the increase incompatibility between the PMMA core and the SFP. Hybrid PS-PM cores wereencapsulated with PS-PMMA-PMAA-PBA copolymer. While PS and PAA enhancedthe compatibility between the CFP and the SFP, PMMA provided goodmechanical properties and PBA lowered the glass transition temperatureof the SFP. To obtain a void-free polymer film by heat processing of thecore-shell particles, the shell thickness was at least 20% of the radiusof core particles.

FIG. 10 shows a typical morphology of the film obtained from theparticles containing CdS-coated PMMA cores. First, to the best of theresolution of laser confocal fluorescent microscopy (LCFM) no distortionin the structure (z vs x-y planes) was observed during annealing.Second, we did not observe any cracking or distortion of the periodicstructure of the array due to at least 26% shrinkage during annealing.Third, the morphology of the film appeared as an inverse of thestructure anticipated in the final stage in Scheme (a) in FIG. 3 a: thedark domains corresponded to the non-fluorescent cross-sections of thePMMA-PMAA latex cores, whereas the bright background corresponded to thePMMA-PBMA matrix doped with fluorescent CdS nanoparticles. The latterfeature could indicate that the NPs detached from the surface of thelatex cores and uniformly mixed with the SFP during polymerization offilm formation.

The need in encapsulation was more rigorous for hybrid microgelparticles because of their hydrophilic nature. FIG. 19 a shows thethermal response of poly(NIPAM-M-HEA) microspheres doped with CdSnanoparticles. Hybrid rnicrogels featured the same variation in D vs Tas the corresponding host microgel particles. The decrease in diameterof the hybrid microgel particles reached up to ca. 55% at 75° C., whichcorresponded to ca. 90% reduction in particle volume in the deswollenstate. A similar size dependence of temperature was observed for themicrogel particles carrying Ag nanoparticles.

Poly(NIPAM-AA-HEA) microspheres doped with CdS and Ag NPs wereencapsulated with hydrophobic shells by copolymerizing methylmethacrylate (MMA), butyl acrylate (BA) and acrylic acid (M) in weightratio 15/4/1 on the surface of the hybrid microgel particles.Interfacial polymerization of poly(MMA-BA-AA) shells was carried out at75° C. and pH=4.2. Under these conditions, poly(NIPAM-AA-HEA)microspheres dramatically shrank and water was expelled from thehydrogel core. Thus polymerization of poly(MMA-BA-AA) inside theparticle core was substantially hindered, and the core-shell structureof the poly(NIPAM-AA-HEA)/poly(MMA-BA-AA) microbeads could beanticipated. The diameter of the core-shell particles varied from 370 to560 nm, thus for the corresponding poly(NIPAM-AA-HEA) cores at 75° C.the thickness of the poly(MMA-BA-AA) shells varied from 95 to 120 nm.Following microgel encapsulation, a yellow dispersion ofCdS/poly(NIPAM-AA-HEA) particles or dark-brown dispersion ofAg/poly(NIPAM-AA-HEA) turned into a stable turbid white latex.Polydispersity of the core-shell particles did not exceed 0.07; thus thenucleation and growth of the secondary poly(MMA-BA-AA) particles werenegligible. The electrokinetic potential of the hybrid core-shellmicrospheres was ca. −55 mV.

FIG. 11 b shows the variation in dimensions of CdS core-shellmicrospheres with the change in temperature. By contrast with microgelmicrospheres, for the entire temperature range (up to 75° C.),regardless of the core composition, no notable change in dimensions ofthe core-shell particles was observed for the time periods exceeding 30min. A similar trend was observed by Lyon et al (J. Wang, D. Gan, L. A.Lyon, M. A. El-Sayed, J. Am. Chem. Soc. 2001, 123, 11284) for themicrogel particles with poly(NIPAM) cores and poly(NIPAM-butylmethacrylate) shells: addition of the small amount of hydrophobicpoly(butyl methacrylate) into the microgel dramatically decreased therate of thermoinduced particle collapse. In the present work, theabsence of thermal response of the hybrid core-shell particles indicatedthat (a) poly(MMA-BA-AA) shells had a dense structure and (b)hydrophilic poly(NIPAM-AA-HEA) cores were screened from the aqueousmedium. A similar screening effect of the shell was observed for thecore-shell particles doped with Ag nanoparticles.

The core-shell particles obtained after encapsulation were used as thebuilding blocks for photonic crystals. FIG. 11 c shows an SEM image ofthe fragment of the colloid crystal obtained from 580-nm size core-shellparticles containing 305 nm-size poly(NIPAM-AA-HEA) cores doped with CdSNPs. FIG. 11 d shows the transmission spectrum for this colloid crystal.The spectrum shows a peak arising from Bragg diffraction from (111)planes of the crystal. The position of the peak at λ_(c)=1354 nm wasused for the estimation of the concentration of CdS nanoparticles in thecore shell-particles. The data were fit to the Bragg law: λ_(c)=1.632d(n_(eff) ⁽²⁾−sin²θ)^(1/2), Miguez, C. López, F. Meseguer, A. Blanco, L.Vazquez, R. Mayoral, M. Ocana, V. Fornes, A. Mifsud, Appl. Ohys. Left.1997, 71, 1148) where n_(eff) is the effective refractive index of thecrystal and d is the diameter of the core-shell sphere. The value ofn_(eff) obtained from data fit was 1.43. It was assumed that the volumefraction of the hybrid polymer spheres in the colloid crystal is 0.74and used the relation n_(eff) ²=0.26 n_(air) ²+(0.74−f) n_(pol)²+fn_(CdS) ² (H. Miguez, C. López, F. Meseguer, A. Blanco, L. Vazquez,R. Mayoral, M. Ocana, V. Fornes, A. Mifsud, Appl. Phys. Lett. 1997, 71,1148) where n_(pol) is the average refractive index of the copolymer inthe core-shell particles, f is the volume fraction of CdS particles inthe colloid crystal, and n_(CdS) is the refractive index of CdS. Forn_(pol)=1.50 (J. Brandrup, E. H. Immergut, i Polymer Handbook, 3^(rd)Ed. John Wiley & Sons, New York, 1989) and n_(CdS)=2.5, (R. H. Perry, D.W. Green, J. O. Maloney, Perry's Chemical Engineers' Handbook, 7 th Ed.McGraw-Hill, New York, 1997 f was found to be 0.03 and volume fractionof CdS in the polymer microspheres was 0.041.

FIG. 12 demonstrates magnetic properties of Fe₃O₄ NPs synthesized in theinterior of 500 nm-size microgels. No hysteresis was observed, that is,both remanence and coercivity were zero, consistent withsuperparagmagnetic properties of magnetite NPs with diameter below 12 nm(Nanomagnetism; Hernando, A., Ed.; Kluwer Academic Publishers:Dordrecht, The Netherlands, 1993; Easom, K. A.; Klabunde, K J.;Sorenson, C. M.; Hadjipanayis, G. C. Polyhedron 1994, 13, 1197-1223). At10 kG, the composite particles had magnetic saturation moment of Ms=32.4emu/g, corresponding to magnetic susceptibility of χ=3.24×10⁻³ emu/(gOe) or χ=0.07 (calculated from the density of bulk magnetite of 5.18g/cm³) ((Nanomagnetism; Hernando, A., Ed.; Kluwer Academic Publishers:Dordrecht, The Netherlands, 1993; Easom, K. A.; Klabunde, K J.;Sorenson, C. M.; Hadjipanayis, G. C. Polyhedron 1994, 13, 1197-1223).Using Ms=92 emu/g of the bulk magnetite, we estimated magneticsaturation moment to be Ms=38.6 emu/g ((Nanomagnetism; Hernando, A.,Ed.; Kluwer Academic Publishers: Dordrecht, The Netherlands, 1993;Easom, K. A.; Klabunde, K J.; Sorenson, C. M.; Hadjipanayis, G. C.Polyhedron 1994, 13, 1197-1223), higher than the experimental valueMs=32.4 emu/g. The decrease in Ms was due to the small NP size (Ziolo,R. F.; Giannelis, E. P.; Weinstein, B. A.; O'Horo, M.; Ganguly, B. N.;Mehrotra, V.; Russell, M. W.; Huffman, D. R. Science 1992, 257, 219;Easom, K. A.; Klabunde, K J.; Sorenson, C. M.; Hadjipanayis, G. C.Polyhedron 1994, 13, 1197). The strategy described herein has severaldistinct features that are particularly attractive for fabrication ofcomposite materials with advanced properties. First, in-situ synthesisof the nanoparticles allows for spatial localization of their nucleationand growth sites thus controlling their size. This feature demonstratedfor synthesis of nanoparticles in POLY(NIPAM-AA-HEA) microgels isintrinsic for synthesis in confined geometries. Moreover, as has beenshown by Antonletti, M.; Grohn, F.; Hartmann, J.; Bronstein, L. (Angew.Chem. Int. Engl. Ed. 1997, 36, 2080) synthesis of inorganicnanoparticles in microgels can produce nanoparticles with peculiargeometries, although these nanoparticles have a larger size than it wasachieved in our work. Therefore, synthesis of nanoparticles in microgelscan be used in it's own right for producing inorganic nanocrystals in aparticular size range. Second, the incorporation of nanoparticles in themicrospheres opens a new avenue for producing hybrid multiscalecomposite materials with periodic structures. A periodic organization ofsubmicrometer core-shell particles leads to a mesoscopic periodicity inthe ultimate material, whereas the diameter of nanoparticles on theorder of several nanometers determines their confined electronic statesand consequently, the spectral properties of their interactions withlight via the quantum size effect.

Recently, hybrid microspheres have been intensively studied, the in-situsyntheses of the nanoparticles on the surface of latex microbeads or inthe bulk of microgels have advantages over the incorporation ofpre-formed nanoparticles: high surface charge, monodipersity of thepolymer microbeads and nanoparticles, and good stability of colloiddispersions. These features are critical for colloid crystal growth. (H.Miguez, F. Meseguer, C. Lopez, A. Blanco, J. S. Maya, J. Requena, A.Mifsud, V. Fornÿs, Adv. Mater. 1998, 10, 480; P. Jiang, J. F. Bertone,K. S. Hwang, V. L. Colvin, Chem. Mater. 1999, 11, 2132; Yin, Y.; Lu, Y.;Gates, B.; Xia, Y. J. Am. Chem. Soc. 2001, 123, 8718; Vickreva, O.;Kalinina, O.; Kumacheva, E. 2000, 12, 110; Kumacheva, E.; Golding, R. K.Allard, M.; Sargent, E. H. Adv. Mater. 2002, 14, 221).

The variation in nanoparticle dimensions allows varying the spectralposition of absorption peak, which would, it turn, change the nonlinearproperties of the material. Moreover, hybriod microspheres can beorganized in a colloid crystals, in the ultimate material thenanoparticles are spatially localized in the periodic array and thematerial enables tunable nonlinear diffraction.

The ability to synthesize very small Fe₃O₄ nanoparticles is what resultsin their exhibiting superparamagnetic properties, which can be used forbiochemical and chemical separation or drug delivery.

Using the method disclosed herein, nanocomposite materials withperiodically modulated magnetic and electric properties can be producedby incorporating metal nanoparticles in different compartments ofmultilayer polymer microbeads. Furthermore, nanostructured materialswith several functions, can be fabricated by employing hybrid core-shellparticles with multilayer structures and/or by doping the cores and theshells of the polymeric spheres with different nanoparticles.

Of key importance in the present invention in the case of both thepolymer microparticles having the nanoparticles incorporated onto theouter surface of the microparticles and the polymer microgel particlesis the ability to tune the material properties of the nanoparticlesdepending on how the particles are treated. The point of treating theparticles is to produce ligands at the surface or in the interior of themicrogel particles which in essence act as nucleation sites for growthof the nanoparticles. In the examples given above the COO— ligands actas the nucleation sites and the microparticles are treated to give aselected concentration of the COO— ligands so they are not too close toeach other (thus causing formation of large particles or precipitationof large particles) and not too far apart to produce too few nucleationsites. As the results in the Examples show, this has an impact on thematerial properties of the nanoparticles including their size,morphology and crystallinity of the nanoparticles. These properties inturn determine the optical, electronic and magnetic properties of themicroparticles which can then be tuned to give particular optical,electronic and magnetic properties depending on the end application forwhich the colloidal particles are being produced.

The ligands in the examples above were COO⁻ produced by deprotonatingCOOH groups present in the polymer constituents making up themicroparticles. In the examples above the COOH were produced by varyingthe ratio of the polymer constituents in the polymer microparticles toeach other.

In the case of the polymer microgel particles an important feature isshrinkage of the doped microgel particles by expulsion of the liquidfrom the microgel particles in which the dispersion is formed, followedby encapsulation of the collapsed microgel particles with a rigid shellthat suppresses stimuli response of the microgel particles. It will beunderstood that the present invention has been exemplified using twoexamples of polymer microgel particles, however, most polymermicroparticles can be converted to a microgel particles if it is exposedto a suitable solvent that results in swelling of the polymerconstituents thus permitting inflow of the ions or molecular complexescontaining the metal species from which the nanoparticles are to begrown.

Prior to encapsulation of the doped polymer microgel particles they aretreated under conditions that lead to their shrinkage and removal ofwater (of any other solvent of which the dispersion is comprised) fromthe interior of the particles thus condensing them. For this reason thepolymer microgel particles are made from stimuli-responsive polymerconstituents (i.e that respond to a change in temperature, pH or ionicstrength of the liquid medium). The hydrophobic shell is used tosuppress interactions between the doped core and the liquid medium (thatis, suppress stimuli response of the doped cores. To make arrays of theparticles a second polymeric shell is formed around each nanoparticlecontaining polymer microgel particles followed by annealing theencapsulated polymer microgel particles together to form the periodicarray.

The present invention has been illustrated using examples in which metalions are incorporated into an electrical double layer formed between thepolymer microparticles and the liquid of the dispersion due to thenegative charge on the COO⁻ligands, Specifically, use has been made ofelectrostatic attachment between anions SO₄ ²— and COO⁻ and cations inthe solution. However, it will be understood that one can use polymerconstituents which include positively charged groups, e.g., imidosole,amino groups, or imino-groups on the polymer and provide electrostaticinteractions with anions.

Further, it will be understood that the present invention is notrestricted to electrostatic interactions for trapping the materialforming the nanoparticles at the surface of the microparticles. Forexample, the dispersion of polymer microparticles may be treated in sucha way as to modify the outer surface of the polymer microparticles toprovide ligands on the outer surface of the polymer microparticles thatcan form a complex with atoms of a metal, ions of the metal, ormolecular moieties containing the metal at the surface of the polymermicroparticle. One then adds atoms of the metal, ions of the metal, ormolecular moieties containing the metal to the dispersion of polymermicroparticles under conditions suitable to facilitate formation of acomplex between the ligands and the atoms of the metal, ions of themetal, or molecular moieties at the surface of the polymermicroparticles. The ligand may be biological in nature which cancoordinate with metals or it may be other organic based ligands otherthan COO⁻. Specific non-limiting examples of this include the formationof complexes between Ni cations and imidozole groups present in one ofthe polymer constituents. Another example may be alginate polymerconstituents in the microparticle will form complexes with Fe³⁺.

The nanoparticles may be comprised of pure metals, compounds includingsemiconductors, dielectric materials, metal hydroxides or metal oxidesto mention just a few. Nanoparticles of metals such as Ag, Au, Co, Ni,Fe have been successfully incorporated into the surface of the polymermicroparticles and interior of the polymer microgel particles. However,the inventors contemplate that in principle most (if not all) metals canbe used as long as the precursor cations are introduced in theelectrolyte medium and specific interactions exit between atoms or ionsof the metals and the functional groups or ligands formed on the surfaceof the polymer microparticles. The most useful metals contemplated bythe inventor to be useful and which may be incorporated include Ag, Au,Co: Ni, Fe, Ag, Au, Co, Mn, Ni, Fe, Pt, Ta, W, Cu, Si, Mo, Zn, Cd, Nb,Y, Ge, Sn, Pb, Al, Ga, In and Ti.

The semiconductor example disclosed herein was CdS but othersemiconductors have also been made including PbS, CdSe and CdTe.Nanoparticles comprising metal oxides such as FeO, Fe₂O₃, but it will beunderstood that oxide nanoparticles may be based on any metal fallwithin the scope of the present invention.

The agent which interacts with the atoms of a metal, ions of the metal,or molecular moieties containing the metal to form nanoparticles may inthe case of metal ions be a chemical reducing agent such as the examplegiven above for reducing silver ions to silver. In addition to achemical reducing agent, light may be used to reduce the metal cationsto produce the pure metal nanoparticles.

In summary, the present invention disclosed herein provides a newstrategy for producing hybrid composite materials, which employsmesoscopic polymeric spheres doped with nanometer inorganic particles.The intrinsic features of our approach are (a) the in-situ synthesis ofthe NPs on the surface of latex microspheres or in the bulk of microgelsand (b) a “core-shell” approach to producing periodically structurescomposite materials. The in-situ synthesis of the NPs in/on themicrospheres provides good control over nanocrystal dimensions and theirconcentration in/on the microbeads. Following synthesis of the NPs,polymer beads can serve as seeds in interfacial polymerization of theshell-forming polymer. The described approach has potential applicationfor producing photonic crystals since (i) polymer microbeads doped orcoated with the NPs are monodisperse, stable, charged, and smooth; thusthey retain their ability to assemble in two- or three-dimensionalarrays; (ii) doping of polymer microbeads with metal and semiconductornanoparticles greatly enhances the refractive index contrast between theparticles and the surrounding medium, e.g., an undoped polymer, thusleading to enhancement of diffraction properties. ((a) Wang, T.; Cohen,R. E.; Rubner, M. F. Adv. Mater. 2002, 14, 1534, (b) Lu, Y.; Yin, Y; Li,Z.; Xia, Y. Nano Lett. 2002, 2, 785 (c) Lin, Y.; Zhang, J.; Sargent, E.H.; Kumacheva, E. Appl. Phys. Lett. 2002, 8, 3134).

Moreover, new properties of such materials can be obtained by combiningtheir structurally and angularly dependent optical properties (arisingfrom optical diffraction) and optical properties of the NPs (arisingfrom the quantum size effect). The proposed approach shows a new avenuefor producing optically responsive materials with periodicitycommensurable with the wavelength of light, an intrinsic property ofphotonic crystals.

It will be understood that instead of embedding nanoparticles on thesurface of the core particles, or in the interior of the polymermicrogel particles, the nanoparticles may be grown in the shell formingpolymer using the same method as growing them in the polymer microgelparticles. Also, the nanoparticles could be grown in the interior of thecore microgel particles and in the shell forming polymer.

As used herein, the terms “comprises”, “comprising”, “including” and“includes” are to be construed as being inclusive and open ended, andnot exclusive. Specifically, when used in this specification includingclaims, the terms “comprises”, “comprising”, “including” and “includes”and variations thereof mean the specified features, steps or componentsare included. These terms are not to be interpreted to exclude thepresence of other features, steps or components.

The foregoing description of the preferred embodiments of the inventionhas been presented to illustrate the principles of the invention and notto limit the invention to the particular embodiment illustrated. It isintended that the scope of the invention be defined by all of theembodiments encompassed within the following claims and theirequivalents.

1-29. (canceled)
 30. A process of synthesizing a composite colloidalpolymer-inorganic material, comprising the steps of: a) synthesizing adispersion of polymer microgel particles in a liquid; b) treating saiddispersion of polymer microgel particles to modify an interior of thepolymer microgel particles to provide an effective concentration ofligands in the interior of the polymer microgel particles, the ligandsbeing selected to form a complex with atoms of a metal, ions of themetal, or molecular moieties containing the metal in the interior of thepolymer microparticle; c) adding atoms of the metal, ions of the metal,or molecular moieties containing the metal to the dispersion of polymermicrogel particles under conditions suitable to facilitate uptake of theatoms of the metal, ions of the metal, or molecular moieties into theinterior of the polymer microgel particles; d) exposing the dispersionof polymer microgel particles to a first effective agent which interactswith the atoms of the metal, ions of the metal, or molecular moieties inthe interior of the polymer microgel particles to form nanoparticles inthe interior of the polymer microgel particles, the nanoparticles beingcomprised of at least the metal, the effective concentration of ligandsbeing selected to give nanoparticles with specified material properties;e) exposing the polymer microgel particles to a second effective agentwhich results in the polymer microgel particles expelling the liquidtherefrom which causes the polymer microgel particles to contract involume; and f) encapsulating the contracted polymer microgel particleswith the nanoparticles in the interior thereof in a protective polymericshell material, the protective polymeric shell material being effectiveto suppress interactions between the contracted polymer microgelparticles and the liquid.
 31. The process according to claim 30including encapsulating the polymer microgel particles with thenanoparticles contained therein in an outer polymeric shell, andannealing the encapsulated polymer microgel particles to form a periodicarray of polymer microgel particles.
 32. The process according to claim30 wherein the specified material properties include size, morphologyand crystallinity of the nanoparticles.
 33. The process according toclaim 30, wherein the step of treating said dispersion of polymermicrogel particles to modify an interior of the polymer microgelparticles provides electrically charged ligands which facilitateformation of an electrical double layer into which ions of oppositeelectrical charge are incorporated.
 34. The process according to claim33 wherein the electrically charged ligands are negatively charged, andwherein the ions of opposite electrical charge are cations of the metal.35. The process according to claim 33 wherein the electrically chargedligands are positively charged, including adding a selected anion to thedispersion wherein the anions coordinate with the positively chargedligands to form a negatively charged ligand-anion complex, and whereincations of the metal are incorporated into an electrical double layerproduced by the negatively charged ligand-anion complex.
 36. The processaccording to claim 34 wherein the cations of the metal are added to thedispersion in a salt of the metal, and wherein the first effective agentis a reducing agent, and wherein the nanoparticles comprise the selectedmetal by itself.
 37. The process according to claim 34, wherein thefirst effective agent includes anions which react with the metal cationsto form a compound, the nanoparticles being comprised of the compound.38. The process according to claim 37 wherein the compound is one of asemiconductor, metal hydroxide and metal oxide.
 39. The processaccording to claim 37 wherein the metal ion is Cd⁺², and the anion isS⁻², and wherein the compound is a semiconductor CdS.
 40. The processaccording to claim 39 wherein the semiconductor is selected from thegroup consisting of CdS, PbS, CdSe and CdTe.
 41. The process accordingto claim 36 wherein the metal is silver and the metal salt is a silversalt, and wherein the nanoparticles are silver nanoparticles.
 42. Theprocess according to claim 41 wherein the Ag nanoparticles exhibitfluorescence upon illumination with UV light.
 43. The process accordingto claim 41 wherein the silver salt is AgNO₃ contained in an aqueoussolution, and wherein the reducing agent is NaBH₄ contained in asolution mixed with the dispersion of core polymer micro particles. 44.The process according to claim 30, wherein the metal is selected fromthe group consisting of Ag, Au, Co, Ni, Fe, Ag, Au, Co, Mn, Ni, Fe, Pt,Ta, W, Cu, Si, Mo, Zn, Cd, Nb, Y, Ge, Sn, Pb, Al, Ga, In and Ti.
 45. Theprocess according to claim 38 wherein the wherein the cations of themetal are added to the dispersion in a salt of the metal, and whereinthe effective agent includes oxide anions which react with the metalcations to form a metal oxide, the nanoparticles being comprised of themetal oxide.
 46. The process according to claim 45 wherein the metal isselected from the group consisting of Ag, Au, Co, Ni, Fe, Ag, Au, Co,Mn, Ni, Fe, Pt, Ta, W, Cu, Si, Mo, Zn, Cd, Nb, Y, Ge, Sn, Pb, Al, Ga, Inand Ti.
 47. The process according to claim 30 wherein the step ofsynthesizing a dispersion of polymer microgel particles includescopolymerization of N-isopropyl acrylamide (NIPAM), acrylic acid (AA),and 2-hydroxyethyl acrylate (HEA) using precipitation polymerization,and wherein the polymer microgel particles contain carboxyl (COOH)groups, and wherein the step of treating the dispersion of polymermicrogel particles in such as way as to ionize the functional groups inthe interior of the polymer microgel particles includes deprotonation ofthe COOH groups to produce charged COO⁻ groups in the interior of thepolymer microgel particles.
 48. The process according to claim 47wherein the step of encapsulating the polymer hydrogel microparticleswith the nanoparticles in the interior thereof in a polymeric shellincludes encapsulating the PNIPAM-PAA-PEHA microgel particles with ahydrophobic poly(methyl methacrylate)-poly(butyl acrylate)-polyacrylicacid shell (weight ratio 15/4/1, respectively).
 49. The processaccording to claim 30 wherein the dispersion is synthesized with thepolymer microgel particles present in an amount of about 1 to about 10wt % of polymer microgel particles.
 50. The process according to claim30 wherein the dispersion is synthesized with the polymer microgelparticles present in an amount of about 1 to about 2 wt % of polymermicrogel particles.
 51. The process according to claim 30 wherein thestep of synthesizing a dispersion of polymer microgel particles includessynthesizing crosslinked poly(styrene-acrylic acid) (PS-PAA) latexmicroparticles and transforming said crosslinked poly(styrene-acrylicacid) (PS-PAA) latex microparticles into microgel particles by exposureto an aqueous solution at sufficiently high pH.
 52. The processaccording to claim 30 wherein the second effective agent includes changein temperature, change in pH or change in ionic strength of the liquidmedium. 53-62. (canceled)